This strikes me as an implementation artifact.  There is no reason for time.strptime() to validate date triplets.  Applications that require valid dates can use datetime.strptime().  I suggest changing time.strptime() specification to match POSIX strptime().  My understanding is that POSIX only requires field by field range checking (%d range 01 to 31, %m range 01 to 12) and not full structure validation.  This would be consistent with the way leap seconds are currently treated:

>>> time.strptime('60', '%S')[5]
60